One of my favourite scenes in Appropriate Behaviour – Desiree Akhavan’s terrific debut film that she directed, wrote and stars in – comes very early in the film. The protagonist Shirin (Akhavan) meets up with Ken (30 Rock’s Scott Adsit), a stoner Brooklynite, in a trendy cafe, in the hope he’ll give her a job. His eyes light up greedily when she mentions that her name is Iranian.

“Iranian! Wow! What do you think of that whole situation?” he coos.

Shirin blinks and tries to come up with an answer (she settles for “It’s a mixed bag”), but Ken has already moved on: “So tell me, what’s the scene like in Tehran? I just read this big article about the underground hip-hop scene in Vice. So you’re part of that?” he asks eagerly.

“No, unfortunately I spend most of my time in Iran watching Disney videos with my grandmother while she untangles jewellery,” she deadpans back.

So it is with some trepidation that I wait to meet Akhavan in a very similar cafe in west Hollywood. I don’t generally expect people to behave like figures from Vice features but, in keeping with her character in the film, the 31-year-old tends to attract some truly cringeworthy stereotyping from other people. This has been going on since she first came to attention with her very funny 2011 web series The Slope, which she made with her then girlfriend Ingrid Jungermann. It poked fun at both gay culture and Brooklyn, and was clearly made by someone who knows both very well.

The cliches, however, have ratcheted up since the Sundance premiere of the critically feted Appropriate Behaviour, the hilarious and moving story of a twentysomething woman trying, not very successfully, to get over a bad breakup while simultaneously hiding her sexuality from her family. The story in the film is total fiction, but there are some personal overlaps between Akhavan and Shirin, and the flurry of press around her can be summed up as: “An Iranian bisexual Lena Dunham!” There is something very odd about how the media will ways in which a young woman is different (Iranian! bisexual!), while at the same time insisting she is exactly like someone else (the new Dunham!).

Akhavan is, to her credit, fairly sanguine about being repeatedly reduced to her nationality and sexuality: “It was a fear I had when making the film, and it really came true. But it’s not such a bad thing. What’s funny is those are the things that made me feel so alienated in my life, and now they’re pulled out as my entire life,” she smiles over a cappuccino.

Slightly more irksome are the frequent references to Dunham, not because she resents her – Akhavan, in fact, plays a recurring character in the fourth series of Girls – but because of the insinuations.

“It’s the idea that there’s room for only one funny woman whose work can be monetised. It happens with any young female film-maker with humour in her work,” she says. “But no one ever looks at [indie film-maker] Alex Ross Perry and says: ‘Oh, another Noah Baumbach!’”

Because American critics have got so caught up in looking for the next Lena Dunham, no one has yet compared Appropriate Behaviour with Annie Hall, which, with its relationship-told-in-retrospect structure, clearly inspired Akhavan. With its emotional sharpness balanced against laugh-out-loud lines, Akhavan’s movie feels a lot more like something by Baumbach or Sarah Polley than the hipster-awkwardness-as-artform seen in Girls. In a strange way, even though Appropriate Behaviour is, on the surface, dealing with issues ostensibly more niche than in Girls (specifically, coping with a traditional Iranian family while being bisexual), it feels more universal, perhaps because struggles with sex and family are more common than the travails of being a middle-class white woman in Brooklyn.

If Appropriate Behavior is part of any trend, it’s that of the rise of smart and funny stories by and about young women, showing that they struggle as much to grow up as male characters have long done in their films. Greta Gerwig in Frances Ha, Kristen Wiig in Bridesmaids, Jenny Slate in Obvious Child and, yes, Dunham in Girls, have all recently explored this area. These stories are very different from the twinkly eyed Kate Hudson chicklit films of the past two decades because the women here are depicted in a far more brutal and honest way: they’re often broke, usually selfish, sometimes cruel, occasionally promiscuous, frequently intoxicated or high and generally pretty confused. They don’t have Bridget Jones’s idealised group of friends, let alone Carrie Bradshaw’s couture wardrobe. Rarely is there a handsome prince at the end of the story who makes everything all right. Instead of looking like perfect princesses, the women in these stories get messy and smelly. But whereas this is the norm for male characters, it is still seen as so anomalous for female characters to look and behave like this that they can be discussed only by comparison with Dunham.

“No good film-maker looks around to see what other people are making and thinks: I’ll make that!” she says. “But things like the manic pixie dream girl, these were the stereotypes that my contemporaries and I grew up with, and there is this influx of narratives because we’re responding to those cliches.”

Akhavan was born in New York in 1983, just a few years after her parents had emigrated from Iran, and raised there. The whole family would learn about the US together by watching western TV shows and movies.

“None of us are alike so if we could settle on a TV show we all liked, it was the best kind of bonding,” she says. While Akhavan and her older brother loved Muriel’s Wedding and Saved By the Bell, her father’s favourite films were by Mel Brooks.

“As soon as my parents moved to New York they very firmly identified as American. It’s not about the shame of being Iranian – it’s about letting go of the past,” she says. “Also my father hasn’t been able to go back to Iran since 1980 and I think it hurts him too much to think about what he left behind, so his identity is firmly American.” To this day, he never follows Iranian news: “He’d rather watch Two and a Half Men or 2 Broke Girls.”

One of the things Akhavan learned about from movies was, of course, sex. So it came as quite a shock when she eventually learned first-hand that sex in real life is not quite how it is in the movies: “I thought: am I crazy? Am I doing it wrong?” she says, still sounding flummoxed. As a result, the sex in Appropriate Behaviour is one of the movie’s great strengths. It’s utterly realistic, not gratuitous or farcical, because Akhavan isn’t interested in the erotics but in the subtle exchanges of power that happen between a couple in bed.

“I really care about how sex is depicted and want to be honest in that arena,” she says, citing Andrea Arnold and Catherine Breillat as inspirations. “That’s why I take my top off in the sex scene because that is absolutely what the character would have done. But now I’m worried people are watching and going: ‘Oh my God, it’s the director’s tits!’”

Akhavan is a delightful coffee companion, exuding the kind of warmth that makes strangers want to tell her their most intimate stories, which she loves. I have to all but physically wrench her back to the interview when she gets distracted by yet another cafe patron who, after eavesdropping on our chat, spends 15 minutes telling Akhavan her life story: “Other people’s stories are so fascinating, don’t you think?” she says, forcing herself to talk about herself again.

So it’s hard to square this warm and sociable young woman with the self-described “weird and ignored” teenager she once was. At school she was, astonishingly, voted ugliest girl and she didn’t make her first friend until she was 14. She didn’t kiss anyone until she was 17, “and that was only because someone dared someone else to kiss me. That’s how much of a weirdo I was.” She then corrects herself: “I actually don’t think I was interesting enough to be weird. I think it’s just that when you’re unattractive and young, you disappear.”

Akhavan is great at capturing the sense of disappearing in her film: Shirin is often not just on the physical outside of parties, but also mentally – you see her getting lost in her own memories, in one instance in the middle of a threesome. “When you’re not the hottest girl in the room at school,” she says, “you get used to being the observer.”

The morning we meet it’s the day after the Independent Spirit Awards, where Akhavan was nominated for best debut script, an experience she describes as “fun and strange. Emma Stone walked into a party I was at and I was like: ‘OK, this party just got too cool for me, I’m done.’”

After school, she went to the all-women university Smith and, once again, she felt like “the ugliest and most ignored student, but for totally different reasons than at school”.

In what sense?

“Because I wasn’t gay enough! I didn’t have a half-shaved head and a pierced septum – that would have made me the coolest girl. It was really funny to go to Smith, where the aesthetic was the opposite of the New York aesthetic, but I was still at the bottom of the totem pole. But it was also kind of great. When you’re constantly on your own, you develop your own criteria about what’s cool.” And one of those things, she decided, was film-making. After doing a film course at college, she went on to study film as a postgrad at NYU, where she met Ingrid Jungermann, and the two fell in love.

Appropriate Behaviour is partly inspired by her breakup with Jungermann, but the film is not, Akhavan frequently stresses, autobiographical. For a start, her parents didn’t react to her coming out the way Shirin’s parents do, but that is not to say that coming out was easy. After she told her parents, they didn’t talk “for a long time”.

“I was heartbroken to have lost my parents, but it was also a really exciting time because I stopped giving a shit about anything. I think all of us are motivated by wanting to do well by our parents – that’s like the universal truth, but especially so for the children of immigrants. I was so driven by it for so long that it literally made me sick at times, and when I let go of that desire my work became 20 times better,” she says.

She made The Slope with Jungermann during this period of near estrangement from her parents, which foregrounded her sexuality and acted as a very public form of coming out. Appropriate Behaviour takes this even further, with relatively more explicit sex and greater emphasis on the emotional bond between Shirin and her ex-girlfriend.

By now, however, her parents have fully accepted their daughter’s sexuality: “It took about a year but my father made the choice to fully embrace me and this public persona I have of being gay. I think we talk about things more openly because of my work,” she smiles, as though that was her intention all along.